Project Summary/Abstract This study's principal hypothesis is that delivering a circadian-effective, tailored lighting intervention (TLI) will reveal a strong association between dose (amount and duration) and improvement in outcome measures of sleep, behavior, and mood among people with Alzheimer's disease (AD) and related dementias (ADRD), with greater responses being associated with greater doses. It is also hypothesized that a longer morning TLI exposure (e.g., 4 h) will be more effective for improving theses outcomes, and that an all-day TLI exposure will result in later bedtimes and greater sleep onset latency. It is further hypothesized that long-term exposure to the TLI will promote better sleep, improved cognition, and reduced depression and agitation compared to control lighting intervention. Preliminary results from an ongoing study of a TLI delivering a fixed amount of circadian stimulus (CS) have demonstrated significant improvements in sleep and behavior in AD/ADRD patients, over both the short (4 weeks) and the long (4 months) term. Elucidating the relationship between the TLI's dose and the study's outcomes will further contribute to the scientific understanding of AD/ADRD while providing a translational component for the development of new lighting products designed to promote sleep and reduce behavioral disturbances in AD/ADRD patients. The study's aims are 3-fold and involve AD/ADRD patients living in controlled environments (memory care, nursing homes, long-term care), examining the TLI's effects on measures of sleep, behavior, and mood. First, a randomized, within-subjects, placebo-controlled study involving 135 participants will investigate the effects of 3 TLI doses, 1 h/day, for 3 consecutive 4-week periods (with 2 intervening 4-week washouts). A second randomized, mixed design, placebo-controlled study involving 135 participants will investigate the effects of a fixed-CS TLI (same as in the ongoing study) of 3 durations (2 h in the morning, 4 h in the morning, and all day) for 2 consecutive 4-week periods (with 1 intervening 4-week washout). A non-active lighting intervention will be used as placebo control for each of the 3 active TLI conditions. A third single-arm, placebo-controlled study involving 200 participants will investigate the impact of the optimal CS dose (amount and duration determined from the first two aims) for a period of 6 months. Participants will be randomly selected to receive either the active or the placebo intervention. The CS dose will be measured in the field for all 3 study aims. The strengths of this project are considerable, as very few instruments are otherwise available to measure personal circadian light exposures and activity patterns. The study population would benefit immensely and immediately from a tailored, non-pharmacological treatment to improve sleep efficiency and consolidation. Effective treatment can significantly reduce the burden on society and, more directly, on caregivers. The expert project team is unique, including a practicing physician/clinician who has access to the population and a team of researchers with expertise in lighting, lighting technologies, sleep, and circadian rhythms.